Expression of DNA sequences in a plant host is dependent upon the presence of operably linked regulatory elements that are functional within the plant host. Choice of the regulatory element will determine when and where within the organism the DNA sequence is expressed. Where continuous expression is desired throughout the cells of a plant, and/or throughout development, constitutive promoters are utilized. In contrast, where gene expression in response to a stimulus is desired, inducible promoters are the regulatory element of choice. Where expression in specific tissues or organs are desired, tissue-preferred promoters may be used. That is, they may drive expression in particular tissues or organs. Such tissue-preferred promoters may be temporally constitutive or inducible. With any of these variables, additional regulatory sequences upstream and/or downstream from a core promoter sequence may be included in expression constructs of transformation vectors to bring about varying levels of expression of nucleotide sequences in a transgenic plant.
Storage protein genes express in embryo and endosperm. In maize they are called zeins and at least about 41 members of the family have been identified in the maize genome. In sorghum the genes are referred to as kafirin genes. Kafirins are classified by their structure, molecular weight and solubility characteristics. Thus α-kafirins have molecular weight of about 25,000 and 20,000, β-kafirins have molecular weight of 20,000, 18,000 and 16,000 while γ-kafirins have a molecular weight of 28,000. By way of example, sorghum α-kafirin genes have been identified by Reddy at GenBank accession number Y17555 (Eddy, E. N. P. “Sorghum bicolor var. INRA450 gene encoding alpha kafirin”) GenBank No. Y17555 (1998)) and Y17556 (Reddy, E. N. P., “Sorghum bicolor var. White Martin gene encoding alpha kafirin” (1998)). Kafirins have been of interest because, among other applications, they can influence digestibility of sorghum grain. Thus there has been interest in modulating expression of such genes.
As this field develops and more genes become accessible, a greater need exists for transformed plants with multiple genes. These multiple exogenous genes typically need to be controlled by separate regulatory sequences however. Further, some genes should be regulated constitutively whereas other genes should be expressed at certain developmental stages or locations in the transgenic organism. Accordingly, a variety of regulatory sequences having diverse effects is needed.
Diverse regulatory sequences are also needed as undesirable biochemical interactions can result from using the same regulatory sequence to control more than one gene. For example, transformation with multiple copies of a regulatory element may cause problems, such that expression of one or more genes may be affected.
Isolation and characterization of a promoter that can serve as a regulatory element for expression of isolated nucleotide sequences of interest in a constitutive manner are needed for impacting various traits in plants. The inventors have isolated just such a promoter.